title: Insights into subunit interactions in the Sulfolobus acidocaldarius archaellum cytoplasmic complex.
abstract: Archaella are the archaeal motility structure that is the functional pendant of the bacterial flagellum but is assembled by a mechanism similar to that for type IV pili. Recently, it was shown by Banerjee et al. that FlaX, a crenarchaeal archaellum subunit from Sulfolobus acidocaldarius, forms a ring-like oligomer, and it was proposed that this ring may act as a static platform for torque generation in archaellum rotation [Banerjee A et al. (2012) J Biol Chem 287, 43322-43330]. Moreover, the hexameric crystal structure of FlaI was solved, and its dual function in the assembly and the rotation of the archaellum was demonstrated [Reindl S et al. (2013) Mol Cell 49, 1069-1082]. In this study, we show by biochemical and biophysical techniques that FlaX from S. acidocaldarius acts as a cytoplasmic scaffold in archaellum assembly, as it interacts with FlaI as well as with the recA family protein FlaH, the only cytoplasmic components of the archaellum. Interaction studies using various truncated versions of FlaI demonstrated that its N- and C-termini interact with FlaX. Moreover, using microscale thermophoresis, we show that FlaI, FlaX and FlaH interact with high affinities in the nanomolar range. Therefore, we propose that these three proteins form the cytoplasmic motor complex of the archaellum.
authors.affiliation: Molecular Biology of Archaea, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany.
authors.forename: Ankan
authors.initials: A
authors.lastname: Banerjee
authors.forename: Tomasz
authors.initials: T
authors.lastname: Neiner
authors.forename: Patrick
authors.initials: P
authors.lastname: Tripp
authors.forename: Sonja-Verena
authors.initials: SV
authors.lastname: Albers
mesh_terms: D019843:Archaeal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002942:Circular Dichroism; D003593:Cytoplasm / Q000378:metabolism*; D005407:Flagella / Q000378:metabolism*; D002479:Inclusion Bodies; D008958:Models, Molecular; D054730:Protein Interaction Domains and Motifs; D021122:Protein Subunits; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism*; D013056:Spectrophotometry, Ultraviolet; D016945:Sulfolobus acidocaldarius / Q000235:genetics / Q000378:metabolism*
chemical_list: D019843:Archaeal Proteins; D021122:Protein Subunits; D011994:Recombinant Proteins
keywords: archaea; archaellum; basal body; flagella; type IV pili